The Virginia State Police trooper killed at a Richmond bus station was the 16th law enforcement officer to die from gunfire this year, compared to seven in the same period of 2015. The 129 percent increase is causing alarm among police.

Chad Dermyer, a 37-year-old veteran of the US Marine Corps, was shot in the chest and killed on Thursday when he approached a man at the Greyhound bus depot as part of a routine exercise in drug interdiction, Virginia State Police said. Two other troopers returned fire and killed the attacker. Two female bus passengers were also injured.

The attacker was identified on Friday as James Brown III of Aurora, Illinois.

"[Brown] has an extensive criminal history in the state of Illinois. He's known to the Aurora Police Department. His history including a variety of illegal gun charges, a variety of violent offenses including gun violence in his history," VSP Superintendent Colonel Steven Flaherty told reporters at a press conference Friday.

Dermyer was one of the dozen state troopers taking part in a specialized training exercise on criminal interdiction at the Greyhound bus depot in Richmond on Thursday. As part of the training, he approached Brown and engaged him in conversation. Brown responded by pulling a .40-caliber pistol and shooting the trooper in the chest.

VSP spokeswoman Corinne Geller would not comment on the apparent motive for the shooting, though Richmond’s WVIR-TV mentioned that Brown’s aunt told media outlets Brown “had a lot of anger” toward police in the past.

Dermyer is the 62nd trooper killed in the line of duty in the 84 year history of the department, according to the VSP.

He is also the 16th officer shot and killed in the line of duty in the US in 2016, according to the National Law Enforcement Memorial Fund, a nonprofit group that tracks police deaths. This is a 129 percent increase from the same period last year, when seven officers were shot and killed.

“Some of these attacks have been launched by Islamic extremists or sovereign citizen types with a hatred of our government; others are being carried out by mentally deranged or coldblooded criminals who see police as the enemy,” Craig W. Floyd, the group’s chief executive, said in a statement on March 18, commenting on the death of Prince George’s PD officer Jacai Colson. “In all cases, our officers are being targeted simply because of the badge that they wear and the job that they do.”

Dermyer served in the US Marine Corps for four years before entering law enforcement. Prior to joining the state police, he worked as an officer in his home town of Jackson, Michigan and in Newport News, Virginia. He is survived by his widow and two young children.

Statistics compiled by the Washington Post show that in the first three months of 2016, police across the US have killed 255 people, 10 more than in the same time period last year.